/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

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 *

 */

#include "memory/allocation.hpp"

#include "runtime/flags/flagSetting.hpp"

#include "runtime/semaphore.hpp"

class ThreadClosure;

class JavaThread;

// A handshake operation is a callback that is executed for each JavaThread

// while that thread is in a safepoint safe state. The callback is executed

// either by the thread itself or by the VM thread while keeping the thread

// in a blocked state. A handshake can be performed with a single

// JavaThread as well.

class Handshake : public AllStatic {

 public:

  // Execution of handshake operation

  static void execute(ThreadClosure* thread_cl);

  static bool execute(ThreadClosure* thread_cl, JavaThread* target);

};

class HandshakeOperation;

// The HandshakeState keep tracks of an ongoing handshake for one JavaThread.

// VM thread and JavaThread are serialized with the semaphore making sure

// the operation is only done by either VM thread on behalf of the JavaThread

// or the JavaThread itself.

class HandshakeState {

  HandshakeOperation* volatile _operation;

  Semaphore _semaphore;

  bool _thread_in_process_handshake;

  bool claim_handshake_for_vmthread();

  bool vmthread_can_process_handshake(JavaThread* target);

  void clear_handshake(JavaThread* thread);

  void process_self_inner(JavaThread* thread);

public:

  HandshakeState();

  void set_operation(JavaThread* thread, HandshakeOperation* op);

  bool has_operation() const {

    return _operation != NULL;

  }

  void process_by_self(JavaThread* thread) {

    if (!_thread_in_process_handshake) {

      FlagSetting fs(_thread_in_process_handshake, true);

      process_self_inner(thread);

    }

  }

  void process_by_vmthread(JavaThread* target);

};